A prior cellular system used a frequency of 2 GHz bands, but a cellular system for next generation mobile communication must use a high frequency of 2-6 GHz bands. As this high frequency has robust straightness, the cellular system for next generation mobile communication has many shadow areas generated by obstacles such as high buildings. Also, as a radio wave of a high frequency band has a large path loss, cell coverage of the cellular system for next generation mobile communication is smaller than that of the prior cellular system. As signal-to-noise ratios (Eb/No) become smaller because of limited power for improved transmission speed of next generation mobile communication, cell coverage becomes increasingly smaller.
For solving coverage or data rate, research regarding low-cost relay stations is progressing according to IEEE 802.16j, WINNER project, etc. Through introducing these relay stations, cell coverage, transmission efficiency, etc., are increased, but it generates many problems such as synchronization, handover, and interference between cells. In particular, technology for handover between a base station and a relay station, and technology for handover between relay stations are necessary. Also, the cellular system may realize distributed multiple antennas through mutual cooperation of the relay stations to get many advantages that can be obtained in the distributed multiple antennas system. However, it reduces resource reuse efficiency and increases interference.